OLDSMOBILE ALERO IDLE AIR CONTROL VALVE PROBLEM

2002 Oldsmobile Alero • 225,000 miles

Why doe idle speed go from 1100 to almost stall rpm and then back up to 1100 repeatedly in park but not in gear? Feathering the throtle will settle out idle speed until moving it to drive then back to park. It does this over and over until it stalls. Other than that it runs out just fine.